Recently, it is expected that the demands for frequencies will rise to keep up with the ubiquitous age. So, the frequencies are regarded as resources having vast economic values and many efforts in a national strategic dimension are being made to the frequency managements by the governments of U.S.A., Great Britain, Japan, and the like. In particular, developments for spectrum managing tools, establishment of extended-term spectrum using plans, promotions in market-directional frequency collection and reassignment policy, unlicensed band extension, and introduction of market-voluntary open frequency policy in command & control are accelerated. And, many countries make aggressive efforts to research and develop the technologies for minimizing interferences with conventional frequencies and the frequency sharing technologies considering locality.
As the wireless communication broadcasting industry has been recently developed, the demands for the frequencies as bases of the corresponding services have risen rapidly. And, the frequency values are rapidly raised.
Since the demand for frequencies was not so high relatively in the past days, a frequency supply to a new service was no big deal. As the demands for frequencies rise explosively nowadays, it is very difficult to supply frequencies to the right places at the right times.
Moreover, there exist preferred bands having excellent radio wave characteristics and the demands for the bands are very high. So, providers often get involved in troubles for the preferred frequency bands.
Hence, frequencies have very high economic values and can be regarded rare resources of limited supplies. And, many efforts are made to research and develop such a new frequency sharing technology as UWB (ultra wide band), CR (cognitive radio), and the like to technically settle the frequency shortage.
The present invention is directed to a problem based on cognitive radio (hereinafter abbreviated CR) as one of the aforesaid radio transmission schemes to use frequencies efficiently in the future. And, the related art communication system and the CR based communication system are schematically explained as follows.
First of all, data transmission and reception are normally implemented by currently serviced radio communication services using fixed bandwidths. In particular, a mobile communication system obtains maximum performance through inter-cell frequency assignment using a resource allocated to a specific band. A scheme of transmitting/receiving a signal using a fixed band has a fixed frame for its implementation. In order to support a higher quality of service (e.g., increasing throughput, increasing a number of users to provide a service, etc.) by fitting a currently used system specifications, a cell structure is normally segmented into small pieces or a new infrastructure is established by expanding old system specifications to keep up with the demand.
In using a frequency resource so far, there are a service system using a fixed bandwidth and a recent service system using a scalable bandwidth that selectively applies one of various bandwidth options.
In determining a standard of a service, the service system using the fixed bandwidth performs a service by forming a standardized frame in a manner of applying various proper transmitting/receiving schemes to the corresponding band. And, a burden of modifying a whole service system in accordance with every variation of the standard is imposed on the service system using the fixed bandwidth.
On the contrary, the standard utilizing the scalable bandwidth is designed to facilitate controls of a variation of a bandwidth and a quality of service rather than the case of the fixed bandwidth. Yet, the scalable bandwidth service operates in a same manner of the fixed bandwidth service in an actual service operation situation. Namely, the scheme for changing a quality of service without increasing complexity of hardware uses the same scheme instead of changing the technique of broadening or narrowing a bandwidth to obtain a result from using the scalable bandwidth.
As mentioned in the foregoing description, as the demand for radio communication services rapidly increases and various techniques appear, a demand for frequencies exceeds a supply. So, there is a problem that there barely exists a band margin available for several GHz bands, in particular, a low frequency band having good frequency characteristics. To solve this problem, CR scheme appears. The CR scheme is proposed by Mitola in 1999 for the purpose of using a frequency band more efficiently. By the CR scheme, a vacant frequency, which is not actually in use, is detected and then shared and used efficiently.
In particular, CR is basically implemented based on software defined radio (SDR). The CR is able to judge and decide whether to set an unused spectrum to a basic communication band by searching spectrum, whether to change a service type by modifying SDR architecture in accordance with a searched service type, or whether to change a quality of service. Considering the basic concepts and the currently active various radio services, it is decided that personally carried wireless terminals converge into one type and it is also expected that a CR terminal will be suitable for the corresponding convergence.
Thus, communication systems according to the currently discussed frequency managing schemes can be categorized into 1) Fixed Bandwidth Communication System, 2) Scalable Bandwidth Communication System, and 3) CR Based Communication System. Ad, their operational systems are schematically explained with reference to the drawings as follows.
FIG. 1 is a diagram to explain a fixed bandwidth service system.
Referring to FIG. 1, a fixed bandwidth service system provides a service using a bandwidth set in an initial standardizing step like a current mobile communication system (CDMA or GSM), a wireless LAN (802.11 or HiperLAN), or a wireless PAN (802.15).
A frequency use approval for the service bandwidth is granted by a government or a predetermined quantity of the service bandwidth is used for a frequency band known in public.
This service, as shown in FIG. 1, is characterized in that there is no increase or decrease of a frequency bandwidth in accordance with time at all and in that a service within a preset bandwidth is optimized within the bandwidth. Hence, FIG. 1 shows that a preset bandwidth keeps being used regardless of a quantity of current traffics.
FIG. 2 and FIG. 3 are diagrams to explain a scalable bandwidth service system.
Scalable bandwidth service systems can be categorized in two types shown in FIG. 2 and FIG. 3, respectively. The two types include a type that a bandwidth used by a terminal is scalable in a state that a service band of a base station is fixed and a type that a bandwidth used by a base station is scalable as well.
First of all, an example that a bandwidth used by a base station is fixed and that a bandwidth serviced for a terminal in the bandwidth of the base station is scalable is shown in FIG. 2. The example of the service includes such a service using OFDM as 902.16, 802.20, and 3GPP LTE or such a CDMA service of assigning a bundle of channels to a terminal as EV-DO and EV-EV. In theses services, a corresponding service is accessed in a manner that a total bandwidth used by a base station is set and that a specific bandwidth is assigned to a bandwidth used by a terminal by a corresponding base station. In this case, a bandwidth to be used by a base station is set in advance in case of system installation.
On the contrary, a case that a bandwidth serviced by a base station varies in accordance with time, as shown in FIG. 3, is possible. This case corresponds to a service model generated when CR is accommodated by 802.22. In particular, an available spectrum per time is detected and a base station extends its service within an available bandwidth. In this case, requirements for a terminal include that the corresponding bandwidth should be entirely accommodated. FIG. 3 exemplarily shows variations of a frequency bandwidth used by a base station and a terminal in accordance with time.
FIG. 4 is a diagram to explain a CR based service system.
Basically, CR does not specify a specific scheme. And, CR means that a configuration of a terminal varies in accordance with a spectrum resource to use a current spectrum resource more efficiently.
FIG. 4 shows how a CR terminal makes an access if there is an unused portion in a spectrum. When there is a spectrum band to be observed, if an unused area is found from the corresponding band, a communication service to be implemented with CR within the area is provided. The communication service can include a fixed band service or a scalable band service. And, the communication service differs from a conventional service in that, since a spectrum varies in accordance with time, a protocol for managing the spectrum variation and a learning process are needed. Moreover, a current standard for implementing CR is 802.22 WRAN system.
Based on the above explanation, the CR can be defined as a technique for transmitting/receiving a radio signal without interference with another device in a manner of cognizing a surrounding radio environment and deciding a communication parameter optimal for a radio environment by itself.
In most countries, personal short-range radio devices use unlicensed frequency bands in general. Yet, a frequency band available without license is limited and the rest of frequency bands are almost assigned to other usages. So, it is difficult to secure a frequency band for a new service. Yet, in the present status of actual frequency use, a situation is a little different. Many frequency bands over 2 GHz are not actually in use and there exist frequency bands not used temporally or spatially in major frequency bands below 1 GHz for TV or mobile communications.
FCC (federal communications commission) performs a study for a real frequency use rate to survey an average frequency use rate varying temporarily or locally. And, the survey says that there is about 15˜85% of a use rate. FCC announces NPRM (notice of proposed rulemaking) to raise frequency use efficiency in December, 2003 to notice redundant use availability for vacant frequencies. Upon this opportunity, the frequency shortage problem can be considerably mitigated.
Since the frequency sharing use availability by CR technique was announced by FCC NPRM in December, 2003, many efforts have been made to develop a real system by a first meeting for IEEE802.22 in November, 2004. This organization discusses standardization for CR applied WRAN on a TV band shown in FIG. 5.
FIG. 5 shows a diagram to explain a CR sharing concept for TV frequency band.
Referring to FIG. 5, IEEE 802.22 provides WRAN service by sharing a TV band. And, a service unit is determined as an integral multiple of an available TV channel (6 MHz TV channel in FIG. 5).
In particular, if there is an unused TV channel, which is indicated as ‘unused TV channel’ in FIG. 5, cognized by a base station, this channel is used for WRAN service. And, if TV channels are consecutively available within a range proposed by a standardization, these channels are combined together to use as a single band. And, a service using the whole is provided. FIG. 5 shows a case that multi-carriers are transmitted to correspond to an unused TV channel environment for example.
And, a terminal cognizes the whole channel status of the base station and should extend its reception capability as well.
Meanwhile, a conventional frequency policy differs per a country or a region in frequency band and frequency assignment specifications for a mobile communication, a wireless LAN and the like. So, in order for a CR terminal to operate correctly, information on a local frequency policy should be retained. Based on this information, when the CR terminal accesses a frequency band in the future, a communication service selection and an operation of a communication system is governed.
However, a method for obtaining information on a frequency policy in a random area is not defined in the conventional frequency policy and the conventional communication method. So, when a power of a CR based terminal is turned on in a random area or a CR based terminal moves away into a random area, the CR based terminal fails to cognize a frequency policy corresponding to the area but is unable to be converted to a communication system suitable for a frequency of the corresponding area.
Moreover, if an open frequency policy depending on a self-regulating market is adopted to proceed instead of adopting a conventional command & control type frequency policy uniformly, the absence of the per area frequency policy information obtaining scheme may cause a considerable problem.